The invention relates to utility vehicles in general, and to skid-steer loaders in particular.
Skid-steer loaders are highly maneuverable, agile, compact vehicles with a wide range of applications in the agricultural, industrial and construction fields. Skid-steer loaders are useful for raising, lifting, carrying, and pushing objects. Their compact nature and low profile allows them to enter enclosed spaces and maneuver under low overhead areas. Their low center of gravity which results from their compact nature also allows them to traverse uneven terrain without overturning.
Skid-steer loaders may include an engine, a boom assembly and an operator""s compartment mounted on a frame supported by four wheels. The engine may be placed in the rear of the skid-steer loader to provide a counterweight for a payload.
The engine powers a main drive system and a lift system for the boom assembly. The direction in which the skid-steer loader travels depends on the angular velocities of the wheels on one side of the vehicle relative to the angular velocities of those on the other side. The skid-steer loader travels in a substantially straight line while the angular velocities of the wheels on both sides of the skid-steer loader are non-zero and relatively equal. The vehicle turns if the angular velocities of the wheels on one side of the vehicle are different than the angular velocities of those on the other side. The vehicle will, in general, turn toward the side of the vehicle on which the angular velocities of the wheels are lower than those of the other side. The degree of curvature of the turn is generally proportional to the magnitude of the velocity differential, after accounting for slippage.
A pair of hydrostatic pumps coupled to hydrostatic motors mounted on the left and right sides of the frame are driven by the engine. The wheels on the left and right sides of the vehicle are driven by the hydrostatic motors through gears, chains, shafts, or sprockets. The angular velocities of the wheels may depend on the volume and direction of flow of the hydraulic fluid supplied to the hydrostatic motors. The volume and direction of flow of the hydraulic fluid supplied to the hydrostatic motors on either side of the skid-steer loader may be controlled from the operator""s compartment by valves actuated by levers.
A boom assembly comprising a pair of lift arms supported by a linkage may be mounted pivotally directly to the main frame, or to a support frame attached to the main frame. The boom assembly generally supports an attachment or implement for lifting, carrying, and pushing objects. Hydraulic lift cylinders coupled to the lift arms or a component of the linkage raise and lower the boom assembly by extending and retracting. The hydraulic lift cylinders are often powered by a hydraulic system that is separate from that used to drive the wheels. This hydraulic system may also power tilt cylinders connected between the boom assembly and the implement.
A separate hydraulic system is usually used in skid-steer loaders to power the boom assembly. This hydraulic system can also be used to actuate one or two tilt cylinders which pivot the implement relative to the lift arms for dumping, leveling, or curling the implement. Hydraulic fluid supplied to the lift and tilt cylinders from an implement pump may be controlled by valves actuated by a pair of foot pedals at the front of the operator""s compartment.
In several aspects, the invention may provide a boom and linkage mechanism for a skid-steer loader which includes a frame having a right and a left side, a right and a left loader arm located respectively on the right and left sides of the frame, each of the right and left loader arms having a forward and a rearward end, an implement vertically pivotally mounted to the forward ends, a pair of tilt actuators respectively connected between the forward ends and the implement, a right forward guide link having a first right lower end portion pivotally connected to the right side of the frame and a first right upper end portion pivotally connected substantially between the forward and rearward ends of the right loader arm, a left forward guide link having a first left lower end portion pivotally connected to the left side of the frame and a first left upper end portion pivotally connected substantially between the forward and rearward ends of the left loader arm, a right rearward guide link having a second right lower end portion pivotally connected substantially proximate to a rear of the right side of the frame and a second right upper end portion pivotally connected substantially proximate to the rearward end of the right loader arm, the second right lower end portion being substantially lower than the first right lower end portion, a left rearward guide link having a second left lower end portion pivotally connected substantially proximate to a rear of the left side of the frame and a second left upper end portion pivotally connected substantially proximate to the rearward end of the left loader arm, the second left lower end portion being substantially lower than the first left lower end portion, a right lift actuator having a first right lower cylinder portion pivotally connected to the right side of the frame between the first right lower end portion and the second right lower end portion, and a first right upper rod portion pivotally connected substantially intermediate between the first right upper end portion and the second right lower end portion, and a left lift actuator having a first left lower cylinder portion pivotally connected to the left side of the frame between the first left lower end portion and the second left lower end portion, and a first left upper rod portion pivotally connected substantially intermediate between the first left upper end portion and the second left lower end portion, wherein the pair of lift actuators extend and retract to raise the pair of loader arms such that the implement moves between a fully lowered position and a fully raised position, and wherein the fully raised position is located substantially vertically above the fully lowered position.